The present invention relates to methods and devices for the heat treatment of metal straps. French Patent Applications 88/00904 and 88/08425 describe methods and devices which make it possible to effect pearlitization and austenitization treatments of metal wires using tubes which contain gases which are practically without forced ventilation.
These methods and devices have the following advantages:
simplicity and low investment and operating expenses since the use of molten metals or salts is avoided, as well as the use of compressors or turbines which would be necessary with forced gas circulation;
a precise law of cooling can be obtained and the phenomenon of recalescence avoided in the case of pearlitization;
the diameter of the wires can be varied within wide limits using the same installation;
in the case of pearlitization, all problems of hygiene are avoided and cleaning of the wire is unnecessary since the use of molten metals or salts is avoided.
The object of the invention is to extend these advantages to the case of the heat treatment of metal straps.
Accordingly, the invention concerns a method for the heat treatment of at least one metal strap, characterized by the fact that the strap is passed through an enclosure containing gas which is practically without forced ventilation in such a manner that a transfer of heat takes place between the strap and the walls of the enclosure by means of the gas contained in the enclosure, and by the fact that the coefficient K.sub.T defined by the equation: ##EQU1## is selected as a function of the heat treatment to be carried out, J being the thickness of the layer of gas between the strap and the enclosure, expressed in millimeters, E being the thickness of the strap, expressed in millimeters, and C being the thermal conductivity of the gas determined at 600.degree. C. expressed in watts.m.sup.-1..degree.K.sup.-1.
The invention also concerns a device for heat treating at least one metal strap, the device being characterized by the following features:
(a) it comprises at least one enclosure containing a gas which is practically without forced ventilation and means which make it possible to pass at least one strap through the enclosure;
(b) the device is so arranged that a transfer of heat takes place between the strap and the walls of the enclosure by means of the gas contained in the enclosure, the coefficient K.sub.T which is defined by the equation: ##EQU2## being selected as a function of the heat treatment to be carried out, J being the thickness of the layer of gas between the strap and the enclosure, expressed in millimeters, E being the thickness of the strap, expressed in millimeters, and C being the thermal conductivity of the gas determined at 600.degree. C. and expressed in watts.m.sup.-1..degree.K.sup.-1.
The invention also concerns metal straps obtained by the method and device in accordance with the invention.
Such straps can be used, for instance, to reinforce articles, in particular pneumatic tires.
The invention will be easily understood by means of the non-limitative examples which follow and the diagrammatic figures relating to these examples.